The present invention relates in general to color marking of selected areas of an anodized layer on a metal article. More particularly, the invention is concerned with production of metal articles having a smooth and durable multi-colored surface, such as an adjustable inner shock absorber tube made of aluminum or aluminum alloy. The shock absorber tube, such as for a bicycle, may have an anodized surface marked with graduations to determine the travel and adjustment of the shock absorber. The selected area or areas to be colored are defined by techniques such as laser etching or mechanical engraving.
Decorated products made of aluminum and its alloys have been produced for many years by first producing an anodized surface on the article. The anodized surface, being porous, may then be dyed and sealed. Lasers have been used to etch selected areas of the surface to expose and restore, to a certain extent, the affinity of the anodized surface to receive dye of other colors so that secondary colors may be applied to the engraved areas which may be once again sealed.
Mechanical engraving has also been used to mark a surface of an article to be colored. When laser etching is used to mark the surface of the article, the heat generated by the laser beam causes the original color to undesirably discolor, become white-on-base, or become metallic silver (the natural color of aluminum). The resulting appearance is rather plain and unattractive.
Various other techniques have been used on sealed and unsealed anodized aluminum surfaces to produce additional visible colored or decoration including application of decals, heat transfer printing, pad printing, silk screen printing, ink jet printing, sublimation printing, mechanical engraving and mechanical stamping. The colors and decorations produced by these techniques have various degrees of surface smoothness and permanency.
U.S. Pat. No. 5,215,864 issued Jun. 1, 1993 to Laakmann is a typical example of prior art which describes multi-coloring an anodized aluminum surface by first dyeing and sealing the surface. Then a laser beam is used to simultaneously unseal and remove dye from selected areas of the surface. A second color is then applied to the laser marked areas. A transparent lacquer can then be applied over the surface of the article to protect and seal the dyes.
The coloration used in the engraved areas produced according to prior art techniques is obtained from water soluble dyes or dyes such as those used in felt tip pens. Such dyes tend to fade quickly when exposed to sunlight. If dye is applied to the etched areas by the manual use of felt tip pens or the like, the process is too slow for economic commercial use particularly when color must be applied to a relatively large surface area. Furthermore, hot water sealing leaches out dye applied to the etched area and requires maintenance of boiling temperature (typically 100xc2x0 C. or 212xc2x0 F.) for well in excess of 15 minutes using de-ionized water at the proper pH to be effective. In addition, hot water sealing involves the potential risk of heat deformation and/or water damage of the article. On the other hand, use of a lacquer spray to seal the colored surface of the article results in a more uneven surface texture on the article.
It is accordingly an object of the invention to provide an improved process of coloring selected areas of anodized surfaces of metal articles which results in a multi-colored smooth durable surface.
The invention provides a process for producing a colored area of desired depth in an anodized layer of a metal article comprising the steps of:
a) defining an area of said layer to be colored by etching said area to a desired depth with a laser beam of selected intensity for a selected time;
b) applying an ink comprised of a polymerizable resin binder and colorant to said area to color said area to said desired depth; and
c) curing said resin binder.